Thank you all for your helpful suggestions.
I guess if these decisions were easy, anybody could make them.
The Z 6 iii is probably the best body for me, along with the FTZ ii to work with my current lenses.
But as the discussion shows, I will most likely need another telephoto zoom, and that's the hard decision. None of them meets my needs. There's a wonderful x to 200 coming out soon, but it would need the teleconverter. The existing 100 to 400 S looks good, but it is very heavy. And so it goes.
Thanks again for the effort you have put into your comments.
--Pieter